A conventional method of producing a sand mold is disclosed in JP 2002-346697A, wherein after a mold space is defined by a flask placed on a pattern plate, a filling frame placed on the flask, and multiple squeeze heads inserted in the filling frame from above, and after the molding sand located at sand ejecting ports of a sand blowing device is fluidized by ejecting a compressed air to the molding sand at that location, a compressed air is supplied to the upper surface of the molding sand in the sand blowing device for a predetermined period of time to blow-charge the molding sand from the sand blowing device into the mold space, and the squeeze heads are lowered to squeeze the molding sand such that the level of the upper surface of the produced sand mold coincides with that of the flask.
However, in the conventional method of producing a sand mold as configured above, the squeeze length of the molding sand varies as the CB value (compactability) of molding sand, which is a property of the molding sand, varies. Thus the level of the upper surface of the produced sand mold tends to be lower or higher than that of the flask.
To attempt to overcome this drawback, the position, or level, of the squeeze heads are changed to change the volume of the mold space. However, if the volume after changed is large, the period of time for blow charging the molding sand, which is the period for supplying a compressed air to the surface of the molding sand, would be short and causes insufficient blow charging.
Further, the inventors of the present invention have developed a molding machine, wherein after upper and lower mold space halves are defined by upper and lower flasks, each formed with a sand blow-in port in its sidewall, a match plate disposed between the upper and lower flasks, and upper and lower squeeze means provided with a plurality of squeeze feet to be inserted in the upper and lower mold space halves from the openings located at one side opposite to the other side of each of the upper and lower flasks located at the match plate, and after molding sand is blow charged from the sand ejecting nozzles of a sand blowing device through sand blow-in ports into the upper and lower mold space halves, the upper and lower squeeze heads are approached each other to compact the molding sand in the mold space halves to produce mold halves. However, since in this conventional molding machine the compressed air is ejected under a high pressure to blow charge the molding sand well, the sand ejecting nozzles tend to be clogged, casing insufficient blow charge and necessitating troublesome cleaning of the nozzles.